[PATCH v2 01/10] ovl: setup overlayfs' private bdi

[Josef Bacik <josef@toxicpanda.com>]

From: Chengguang Xu <charliecgxu@tencent.com>

Setup overlayfs' private bdi so that we can collect
overlayfs' own dirty inodes.

Signed-off-by: Chengguang Xu <charliecgxu@tencent.com>
[josef: only for an overlay that tracks dirty inodes, add
 ovl_tracks_dirty()]
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/overlayfs/overlayfs.h | 17 +++++++++++++++++
 fs/overlayfs/super.c     |  7 +++++++
 2 files changed, 24 insertions(+)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 92da556598da..aa6c2d005a40 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -7,6 +7,7 @@
 #include <linux/kernel.h>
 #include <linux/uuid.h>
 #include <linux/fs.h>
+#include <linux/backing-dev.h>
 #include <linux/fsverity.h>
 #include <linux/namei.h>
 #include <linux/posix_acl.h>
@@ -663,6 +664,22 @@ static inline bool ovl_should_sync(struct ovl_fs *ofs)
 	return ofs->config.fsync_mode != OVL_FSYNC_VOLATILE;
 }
 
+/*
+ * Does this overlay track the upper inodes that are modified through it, so
+ * that syncfs() and unmount only have to sync those?
+ *
+ * There is nothing to track without an upper filesystem, and a volatile overlay
+ * never syncs.  sync_filesystem() does not write any inodes of a filesystem
+ * that has no writeback, like tmpfs, and nothing ever clears their dirty flags.
+ */
+static inline bool ovl_tracks_dirty(struct ovl_fs *ofs)
+{
+	if (!ovl_upper_mnt(ofs) || !ovl_should_sync(ofs))
+		return false;
+
+	return ovl_upper_mnt(ofs)->mnt_sb->s_bdi != &noop_backing_dev_info;
+}
+
 static inline bool ovl_should_sync_metadata(struct ovl_fs *ofs)
 {
 	return ofs->config.fsync_mode == OVL_FSYNC_STRICT;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 19b6d54c4500..ce3e30235ae9 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1455,6 +1455,13 @@ static int ovl_fill_super_creds(struct fs_context *fc, struct super_block *sb)
 		if (err)
 			return err;
 
+		/* Dirty overlay inodes go on the lists of this bdi */
+		if (ovl_tracks_dirty(ofs)) {
+			err = super_setup_bdi(sb);
+			if (err)
+				return err;
+		}
+
 		upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
 		if (!ovl_should_sync(ofs)) {
 			ofs->errseq = errseq_sample(&upper_sb->s_wb_err);

-- 
2.55.0